Ekko ult to function like ezreal E?
Right now I find that 
's untargetability on his ult is pretty strong. Though, at the same time you would not want it to be interruptable.
So i racked my brains and thought of ezreal's unique interaction with spells like blitzkrank pull etc.
As such if your damage would kill him if he'd not of gone untargetable then he would die. It would be such that you shouldnt risk being too low when ulting on him. still incurs the damage but wherever he was relocated.